Refrigeration appliance and method for operating a refrigeration appliance

Abstract

The invention relates to a refrigeration appliance (11) comprising: a refrigeration circuit operated by means of a linear compressor (1, 1'); and a control unit (10) that is designed to control an operating frequency (fw) of a piston (3) of the linear compressor (1, 1'), which piston is driven by means of at least one drive magnet (9) equipped with at least one drive coil (9A), in such a way that the linear compressor (1, 1') achieves minimal power consumption (Pmin). The invention also relates to a method for operating a refrigeration appliance (11) equipped with a refrigeration circuit operated by means of a linear compressor (1, 1'), in which method an operating frequency (fw) of a piston (3) of the linear compressor (1, 1') is controlled in such a way that the linear compressor (1, 1') achieves minimal energy consumption (Pmin). The invention can be particularly advantageously applied to household refrigeration appliances.

Description

[0001] Cooling device and method for operating a cooling device

[0002] The invention relates to a refrigeration device with a refrigeration circuit operated by a linear compressor and with a control or regulation system configured to regulate the operating frequency of a piston or cylinder of the linear compressor. The invention also relates to a method for operating a refrigeration device equipped with a refrigeration circuit operated by a linear compressor, in which the operating frequency of a piston or cylinder of the linear compressor is regulated. The invention is particularly advantageously applicable to household refrigeration devices.

[0003] Cooling devices are known whose refrigeration circuit uses a linear compressor as the drive. To achieve low energy consumption, the operating frequency of the piston is adjusted so that a predetermined resonance frequency of the oscillating system is matched as accurately as possible. The linear compressor is thus operated at a constant, predetermined operating frequency. Implementing this method in production requires that every linear compressor of the same type exhibit the predetermined resonance frequency as accurately as possible, which poses a major challenge for production and assembly because tolerances must be maintained within strict limits. Furthermore, the resonance frequency can change depending on load and temperature.Consequently, it often happens that the actual resonance frequency deviates from the predetermined resonance frequency, resulting in increased energy losses during operation of the linear compressor.

[0004] It is the object of the present invention to at least partially overcome the disadvantages of the prior art and in particular to provide a simple, reliable and energy-saving way of operating a linear compressor of a refrigeration device.

[0005] This object is achieved according to the features of the independent claims. Preferred embodiments are particularly evident in the dependent claims. This object is achieved by a refrigeration device with a refrigeration circuit operated by a linear compressor and with a control system configured to adjust or control an oscillation or operating frequency of a piston or cylinder of the linear compressor such that the power consumption of the linear compressor is in the range of minimum power consumption.

[0006] This provides the advantage that the operating frequency is automatically adjusted to minimize the linear compressor's power consumption. This avoids the aforementioned problems of the state-of-the-art compressors during operation.

[0007] For example, in addition to the linear compressor, the refrigeration circuit may comprise at least one evaporator, at least one expansion medium and at least one condenser in a basically known manner.

[0008] The invention relates both to a linear motor in which the piston is driven as a lifting body and moves relative to the cylinder as a stationary component, and to a linear motor in which the cylinder is driven as a lifting body and moves relative to the piston as a stationary component.

[0009] The piston is arranged in a cylinder in a housing of the linear compressor. The piston and cylinder are mounted so that they can be moved longitudinally relative to one another, with one of the two being immobile in the cooling unit and relative to a coil of the motor, and the other being movable as a lifting body. The lifting body is articulated relative to the immobile component by at least one elastic spring element. The lifting body, which is equipped with at least one permanent magnet, is typically driven by the magnetic field of at least one electromagnet, which is equipped with at least one coil ("drive coil") operated with an alternating electrical voltage, and is thereby set into oscillation. Depending on the direction of movement, a working volume delimited by the cylinder and one end face of the piston is increased or decreased. If the working volume is increased, cooling or heating energy is generated.Working fluid is drawn into the working volume at an inlet from a refrigeration circuit connected to the working volume. If the working volume is then reduced again, the working fluid is forced into the refrigeration circuit at an outlet. The amplitude of the alternating voltage determines the stroke of the reciprocating element, which in turn determines the mass flow of the working fluid in the refrigeration circuit. In the steady state, the operating or oscillation frequency of the reciprocating element is determined by the voltage frequency of the alternating voltage signal. The efficiency of the linear compressor depends on the voltage frequency and thus the operating frequency. The basic operation of a linear compressor in a refrigeration circuit of a refrigeration appliance is well known and will therefore not be discussed further here. The linear compressor can also be viewed as a linear motor, whose reciprocating element corresponds to the rotor or "mover."

[0010] The stroke of the lifting body can be understood in particular as the deflection of the lifting body from its rest position, especially "forward," whereby the working volume is then compressed. This can also be understood as the direction of movement in the direction of inlet and outlet. The stroke of the lifting body can be understood specifically as the deflection of the lifting body up to its forward reversal point, i.e., the position at which the lifting body is maximally deflected forward.

[0011] The fact that the control is designed to regulate the oscillation or working frequency of the reciprocating body in such a way that a power consumption of the linear compressor results in a range of minimum power consumption is based on the fact that the working frequency is not set constantly, but is automatically adjusted using at least one feedback variable in such a way that a minimum power consumption of the linear compressor results.

[0012] The minimum power consumption can be an absolute minimum or a local minimum, particularly in a frequency band of the operating frequency between 10 Hz and 200 Hz. The minimum power consumption can occur, in particular, at an operating frequency that corresponds to the resonant frequency or lies within a frequency range around the resonant frequency, for example, within + / - 8 Hz of the resonant frequency. The operating frequency is adjusted, in particular, while maintaining or keeping constant one or more adjustable target variables, such as the stroke of the lifting body, the amplitude of an electrical excitation signal such as an excitation current, etc.

[0013] In addition to or as an alternative to power consumption, energy consumption can be used to control the linear compressor. Power consumption and energy consumption are interchangeable for defined periods of time and can therefore be used interchangeably unless otherwise stated. Power consumption can also be referred to as power input, and energy consumption can also be referred to as energy input.

[0014] One embodiment is that the control system is configured to regulate or adjust the operating frequency in such a way that minimal power consumption of the linear compressor is achieved. This is advantageously particularly energy-saving. The minimum power consumption corresponds, in particular, to the minimum that can be achieved as precisely as possible by the control system.

[0015] In one embodiment, the control is set up to regulate the working frequency such that it has a specific frequency difference from the working frequency with minimal power consumption. This has the advantage that the linear compressor can still be operated with a low power consumption close to the minimum, but a noticeably higher reciprocating body stroke can be achieved due to the frequency difference. In one development, the working frequency is higher by a specific frequency difference than the working frequency with minimum power consumption. In one development, the frequency difference is not more than 6 Hz, in particular in a range between 1 Hz and 6 Hz, in particular in a range between 2 Hz and 5 Hz.

[0016] In one embodiment, the control system is configured to calculate a target AC voltage for the at least one drive coil of the at least one drive magnet from the currently set operating frequency and a target stroke of the lifting body. This is advantageously particularly easy to implement and enables simple implementation of a variation of the operating frequency of the lifting body. The characteristic variables of the target AC voltage can include, for example, a voltage frequency and the voltage amplitude. The target AC voltage can be applied as a sinusoidal voltage signal or as a pulsed, e.g., pulse-width-modulated, voltage signal.

[0017] In one embodiment, the control system is designed to calculate the power consumption of the linear compressor for a set operating frequency from a setpoint voltage signal for the at least one drive coil and a measured actual power consumption of the at least one drive coil. This offers the advantage of simple implementation with precise determination of the electrical power currently consumed by the linear compressor at the set operating frequency. This exploits the fact that the setpoint voltage signal can be implemented very precisely, i.e. there is only a slight to practically no difference between the setpoint value and the actual value. Therefore, a voltmeter for the linear compressor, in particular for its drive coil(s), can be dispensed with, and only an ammeter for the current flowing through the linear compressor, in particular its drive coil(s), is required.

[0018] Alternatively, the voltage signal applied to the linear compressor or the at least one drive coil can be measured, which advantageously allows its more precise determination.

[0019] A further development involves calculating the electrical power by averaging the alternating voltage or voltage signal and the measured current over a specific period of time. This advantageously enables a particularly robust and reliable power determination.

[0020] It is a further development that the averaging is a quadratic averaging, whereby the consumed electrical power P is then calculated from the effective values ​​of the voltage signal and the measured current.

[0021] The period used for averaging can include one or more periods of the voltage signal.

[0022] In one embodiment, the control system is configured to vary the operating frequency by means of an iteration method, in particular an approximation method, towards minimum energy consumption, and to set the operating frequency to the consumption-optimal operating frequency found by means of the iteration method (i.e., the operating frequency at which minimum power consumption results). The consumption-optimal operating frequency can correspond to the resonant frequency, but this is not necessary. The minimum power consumption can occur, in particular, at an operating frequency that corresponds to the resonant frequency or lies within a frequency range around the resonant frequency, for example, within + / - 8 Hz of the resonant frequency.

[0023] If a specific frequency offset is to be added, this can be done in addition to the consumption-optimal operating frequency found using the iteration method.

[0024] In one embodiment, the control system is configured to vary the target operating frequency and regulate it to a value (the "consumption-optimal" frequency or operating frequency) at which a minimum energy consumption of the linear compressor, determined from the variation, results. By using a variation method, the consumption-optimal frequency can advantageously be determined reliably and with comparatively little effort under virtually all boundary conditions and manufacturing tolerances. To implement the variation method, any suitable iteration algorithms for determining minimum values ​​can be used, especially approximation or approximation algorithms that approximately solve the optimization problem at hand. If a specific frequency offset is to be added, this can be done in addition to the consumption-optimal operating frequency determined using the iteration method.

[0025] One embodiment is that the control system is configured to vary the set operating frequency (previously considered optimal for consumption) again after a specified period of time. This offers the advantage that the previously determined and set optimal operating frequency can be regularly adjusted to possible changes in the boundary conditions. The period can range, for example, from 15 minutes to several hours, but is not limited to this.

[0026] In one embodiment, the control system is configured to vary the set operating frequency again if the electrical power consumed reaches or exceeds a predetermined threshold, in particular with respect to the previously determined power or the previously determined power consumption. The electrical power consumed is advantageously a particularly good indicator that the operating conditions of the linear compressor have changed noticeably. In a further development, this embodiment can also be expressed in such a way that the control system is configured to vary the set operating frequency again if the electrical power consumed reaches or exceeds an upper threshold or reaches or falls below a lower threshold, in particular deviates significantly from the previously determined power.In a further development, this can also be expressed by the controller being configured to vary the set operating frequency again if the calculated power falls or falls outside a specific band or range around the previously determined minimum power. In a further development, the previously determined consumed power corresponds to the previously determined minimum power consumption or the power consumption at the operating frequency that, in contrast, has the specified frequency difference.

[0027] In one embodiment, the control system is configured to vary the set operating frequency again if the specified target stroke of the reciprocating body has been changed. The target stroke of the reciprocating body may, for example, have been changed to increase cooling capacity, for example, if a target cooling chamber temperature of the refrigeration unit has been lowered. The target stroke of the reciprocating body may, for example, be set using a control system for the linear compressor, in particular its drive magnet or its drive coil(s). The control system may also include the control of the operating frequency.

[0028] In one embodiment, the control system is configured to vary the operating frequency again if a change in temperature and / or load reaches or exceeds a predetermined threshold. This advantageously enables an adjustment of the consumption-optimized operating frequency if certain boundary conditions change significantly. The temperature can include a temperature of the working fluid, a temperature of the linear compressor or in the vicinity of the linear compressor, and / or a cooling chamber temperature. The load depends in particular on the intake pressure at the inlet to the working volume and on the discharge pressure at the outlet.

[0029] One embodiment is that the control system is configured to specify a precalculated resonance frequency of the lifting body as the initial value of the iteration process when the operating frequency begins or is varied again. This prevents an unwanted drift of the initial value over a longer period of time. A further development is that when the cooling device is switched on, the iteration process is started with the precalculated resonance frequency, and subsequent iteration processes begin with the last determined consumption-optimal operating frequency as the starting value.

[0030] One embodiment of the control system is designed to continuously perform the iteration process. This achieves the advantage that the energy or power consumption of the linear compressor remains virtually constant at a minimum. In particular, after the operating frequency with optimal consumption has been found, the operating frequency is immediately varied again using this as a starting value.

[0031] In one embodiment, the cooling appliance is a household appliance with a cooling device, in particular a household cooling appliance such as a refrigerator, a freezer or a combination thereof, an air conditioner, a laundry treatment appliance or a dishwasher.

[0032] The problem is also solved by a method for operating a refrigeration device equipped with a refrigeration circuit operated by a linear compressor, in which the operating frequency of a reciprocating body of the linear compressor is controlled such that the energy consumption of the (operated or working) linear compressor is in the range of minimum energy consumption. The method can be designed analogously to the refrigeration device, and vice versa, and has the same advantages.

[0033] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following schematic description of an embodiment, which is explained in more detail in connection with the drawings.

[0034] Fig.1 shows a sectional side view of a sketch of a possible linear compressor with driven piston;

[0035] Fig.2 shows a plot of the power consumption of a motor of a linear compressor installed in a refrigerator against the set operating frequency;

[0036] Fig.3 shows a control system for regulating the operating frequency; and Fig.4 shows a sectional side view of a possible linear compressor with a driven cylinder.

[0037] Figure 1 describes a linear motor in which the piston, acting as a reciprocating body, is driven and moves relative to the cylinder, a stationary component. Figure 4 describes a linear motor in which the cylinder, acting as a reciprocating body, is driven and moves relative to the piston, a stationary component. Figures 2 and 3 apply to both motor variants.

[0038] Fig. 1 shows a sectional side view of a sketch of a possible linear compressor 1. The linear compressor 1 has a cylinder 2 rigidly connected to the housing 20 in a housing 20, and a piston 3 which is linearly displaceable in the cylinder 2, as indicated by the double arrow, and is provided with permanent magnets 3A. The rear side of the piston 3 is hinged to the housing 20 via a spring element 4 and the front side of the piston 3 delimits a working volume 5. A unidirectional inlet 6, through which the working medium 7 can flow into the working volume 5, and a unidirectional outlet 8, through which the working medium 7 can flow out of the working volume 5, open into the working volume 5. The linear compressor 1 also has an electromagnet or drive magnet 9 arranged outside the cylinder 2.The drive magnet 9 has a drive coil 9A, which is typically operated on the basis of an alternating voltage U~, and a stator 9B made of magnetic material, e.g. made of sheet steel segments, and then exerts a magnetic force on the permanent magnets 3A, whereby the piston 3 as a lifting body 23 is excited to oscillate linearly in the cylinder 2. When moving forward or towards the spring element 4, the oscillating piston 3 elastically expands the spring element 4 and reduces the working volume 5, so that the working medium 7 is pressurized and flows out through the outlet 8 against a final pressure. Flow out through the inlet 6 is prevented, e.g. by a one-way valve. In the opposite direction towards the rear or towards the spring element 4, the lifting body 23 elastically compresses the spring element 4 and increases the working volume 5, so that a negative pressure is created there.The negative pressure, in turn, causes the working medium 7 to flow through the inlet 6 against the suction pressure. Inflow through the outlet 8 is prevented, e.g., by a one-way valve. The inlet 6 and the outlet 8 can, for example, both be arranged on a front-end valve plate 2a. The vibration system, which includes at least the lifting body 23 and the spring element 4, has a specific resonance frequency f. res At a constant alternating voltage U~, a uniform back and forth movement of the piston 3 occurs with a specific piston stroke A and a specific oscillation or working frequency f w So far, the resonance frequency f res for a specific linear compressor 1 type-related in advance (e.g. by solving a system of equations or a simulation program) and the alternating voltage U~ is set so that the working frequency f w the precalculated resonance frequency f res meets.

[0039] The control of the linear compressor shown in Fig. 1 and the linear compressor shown in Fig. 4 is explained with reference to Fig. 2 and Fig. 3. The positions x, xo and reversal points x+, ma x, x., ma x of the lifting body refer to the front of the movable piston 3 with respect to the linear compressor 1 according to Fig.1, and to the cylinder bottom 21 of the movable cylinder 2' with respect to the linear compressor T according to Fig.4.

[0040] Fig.2 shows a plot of the power consumption P of a linear compressor 1 installed in a cooling device against the set operating frequency f w . It is currently assumed that in a certain frequency range around the resonance frequency f res around a curve K of the power consumption P against the operating frequency f w the frequency as shown schematically at f res a minimum P m in and, starting from this, with a larger frequency spacing to fres steadily increasing. However, it has been shown that the consumption-optimal operating frequency f opt , at which the electrical energy or power consumption of the linear compressor 1 is minimal, does not necessarily correspond to the exact resonance frequency f res of the oscillation system, but the relationship f opt = f res only applies to certain operating conditions. In addition, the resonance frequency f res change due to changes in external influences.

[0041] Fig.3 shows a control 10 for controlling the working frequency f w of the linear compressor

[0042] 1, which, like the linear compressor 1, can be a component of a cooling device 11, e.g., a household refrigerator. A target stroke Aref for the lifting body 23 is specified to the control system 10, e.g., via a control device of the cooling device 11. The target stroke A ref is combined with a specific or desired operating frequency f w a first module ("amplitude control module") 12, which then generates the corresponding or "correct" target alternating voltage U~, re f is calculated for the drive coil 9A. The target AC voltage U~,ref is fed to a second module (pulse width or "PWM module") 13, which calculates the target AC voltage U~, re f corresponding current pulses are generated to energize the drive coil 9A.

[0043] The target alternating voltage U~ specified for the PWM module 13, ref, as well as the current eas of the current pulses output to the drive coil 9A, measured by a current sensor 14, is fed to a third module ("power calculation module") 15, which calculates the electrical power P (t) consumed by the linear compressor 1, or alternatively, the electrical energy consumed over a specific period of time. The consumed electrical power P (t) can be determined, for example, by averaging the desired AC voltage U~, re f and the measured current Leas over a certain period of time, in particular by quadratic averaging. The consumed electrical power P (t) can thus be calculated in particular from the effective values ​​of U~, re f and Leas are calculated. The period used for averaging can be one or more periods of the target AC voltage U~, re f include.

[0044] The consumed electrical power P is fed to a fourth module ("frequency control algorithm") 16, which uses the knowledge of the consumed electrical power P to determine the operating frequency f w until the minimum power consumption P (t) = Pmin is reached.

[0045] This can be done, for example, by means of an iterative process in the form of an approximation method that exploits the fact that, starting from a minimum power consumption Pmin at f O pt the consumed power P with larger frequency separation of the operating frequency f w to f O pt increases continuously. The approximation method can, for example, be implemented in such a way that for a starting value fo of the operating frequency f w the electrical power Po (fo) consumed at this frequency is determined and this pair of values ​​(fo; Po) is stored. For a next step, f w= fi = fo + Af with Af > 0 a suitable step size. If the corresponding consumed electrical power Pi (fi) > Po (fo), then f w = f 2 = fo - Af. If P2 (f2) > Po (fo), either fo can be used as the consumption-optimal operating frequency f opt or this iteration can be repeated for a smaller step size Af with Af > Af > 0. However, if the power P1 is Pi < Po, then f w = f 2 = f 1 + Af. This process is repeated until Pj (f) > Pu (fn). Then, either fn can be set as the consumption-optimal operating frequency f opt or the iteration can be repeated starting at fn for a smaller step size Af. This approximation method can be used for both directions of f wbe performed equivalently. Furthermore, other iteration schemes can also be used, such as the Newton method or variants thereof.

[0046] In addition, it is possible to continue the iteration process, in particular the approximation method, after finding a consumption-optimal operating frequency f opt to be triggered again, for example after a specified period of time, event-triggered, e.g. with a change in the electrical power consumed, a temperature and / or load above a certain threshold, or immediately in order to achieve a practically continuous iteration.

[0047] Of course, the present invention is not limited to the embodiment shown.

[0048] In general, "a", "an", etc., can be understood as a singular or a plural, in particular in the sense of "at least one" or "one or more", etc., unless this is explicitly excluded, e.g. by the expression "exactly one", etc.

[0049] A numerical value may also include the exact number stated as well as a usual tolerance range, as long as this is not explicitly excluded.

[0050] Fig. 4 shows a sectional side view of a sketch of an alternative possible linear compressor T. The linear compressor T has a cylinder 2' within a housing 20' of the linear compressor T, which cylinder, as indicated by the double arrow, is linearly displaceable relative to the piston 3', which is rigidly connected to the housing 20'. A side wall of the cylinder 2' and a cylinder base 21 act as movable walls, together with a front side of the piston 3' as an immovable wall, delimit a working volume 5. The cylinder 2' is provided with permanent magnets 3A which are arranged on a cylinder frame 22. The cylinder frame 22 extends the cylinder 2' beyond the cylinder base 21 relative to the working volume. The cylinder 2' is hinged to the housing 20' by means of the cylinder frame 22 via a spring element 4. During operation, the cylinder 2' moves as a lifting body 23 relative to the piston 3' as a stationary component.A unidirectional inlet 6 opens into the working volume 5, through which a working medium 7 can flow into the working volume 5, and a unidirectional outlet 8, through which the working medium 7 can flow out of the working volume 5. The linear compressor 1 also has an electromagnet or drive magnet 9 arranged outside the housing 20'. The drive magnet 9 has a drive coil 9A, which is typically operated on the basis of a possibly pulsed alternating voltage U~, and a stator 9B made of magnetic material, e.g., sheet steel segments. The operated drive magnet 9 exerts a magnetic force on the permanent magnets 3A' of the cylinder 2', whereby the lifting body 23 is excited to linearly oscillate relative to the rigid piston 3'. With a constant alternating voltage U~, the lifting body 23 moves back and forth with a certain oscillation or working frequency f. wwhich at least approximately corresponds to the voltage frequency of the alternating voltage U~. In particular, the operating frequency f w a resonance frequency f res of a vibration system comprising at least the lifting body 23 and the spring element 4.

[0051] The oscillating cylinder 2 elastically expands the spring element 4 upon movement forward or toward the spring element 4 and reduces the working volume 5, so that the working medium 7 is pressurized and flows out through the outlet 8 against a final pressure. Outflow through the inlet 6 is prevented, e.g., by a one-way valve. In the opposite direction, toward the rear or toward the spring element 4, the cylinder 2 elastically compresses the spring element 4 and increases the working volume 5, creating a negative pressure there. The negative pressure, in turn, causes the working medium 7 to flow in through the inlet 6 against an intake pressure. Inflow through the outlet 8 is prevented, e.g., by a one-way valve. The inlet 6 and the outlet 8 can, for example, both be arranged on a valve plate 2A on the end face of the piston 3'. List of Reference Symbols

[0052] 1, T Linear compressor

[0053] 2, 2' cylinder

[0054] 2a Valve plate

[0055] 3, 3' pistons

[0056] 4 spring element

[0057] 5 Working volume

[0058] 6 Entrance

[0059] 7 Working medium

[0060] 8 Outlet

[0061] 9 Drive coil

[0062] 10 Regulation

[0063] 11 Cooling device

[0064] 12 Amplitude control module

[0065] 13 PWM module

[0066] 14 Current sensor

[0067] 15 Performance calculation module

[0068] 16 Frequency control algorithm

[0069] 20, 20' housing

[0070] 21 Cylinder base

[0071] 22 cylinder frames

[0072] 23 lifting bodies

[0073] A piston stroke

[0074] Aref Target piston stroke fopt Consumption-optimized operating frequency f w Working frequency

[0075] Imea's actual current

[0076] K History

[0077] P Power consumed

[0078] Pmin Minimum power

[0079] U~ Alternating voltage x+,max Front reversal point of the lifting body x+,max ref Front target reversal point of the lifting body x.,max Rear reversal point of the lifting body xo Rest position of the lifting body

Claims

Patent claims 1. Cooling device (11) with a refrigeration circuit operated by means of a linear compressor (1 , T) and with a control (10) which is designed to set an operating frequency (f w ) of a piston (3) or cylinder (2') driven by means of at least one drive magnet (9) equipped with at least one drive coil (9A) as a lifting body (23) of the linear compressor (1 , T) in such a way that a power consumption (P) of the linear compressor (1 , T) results in the range of a minimum power consumption (Pmin).

2. Cooling device (11) according to claim 1, wherein the control (10) is arranged to control the working frequency (f w ) in such a way that a minimum power consumption (Pmin) of the linear compressor (1 , T) is achieved.

3. Cooling device (11) according to claim 1, wherein the control (10) is designed to control the operating frequency (f w) so that they have a certain frequency difference from the working frequency (f w ) with minimal power consumption (P m in), in particular is greater by a certain frequency spacing than the operating frequency (f w ) at minimum power consumption (Pmin), in particular not more than 6 Hz.

4. Cooling device (11) according to one of the preceding claims, wherein the control (10) is designed to determine from the set operating frequency (f w ) and a desired stroke (Aref) of the linear compressor (1 , T) to calculate a desired alternating voltage (U~) for the at least one drive coil (9A).

5. Cooling device (11) according to claim 4, wherein the control (10) is designed to operate at a set operating frequency (f w) to calculate the power consumption (P) of the linear compressor (1, T) from a desired voltage amplitude for the at least one drive coil (9A) and a measured actual current consumption (eas) of the at least one drive coil (9A).

6. Cooling device (11) according to claim 5, wherein the control (10) is arranged to control the operating frequency (f w ) using an iteration method, in particular an approximation method, to a minimum energy consumption (P m in) and the working frequency (f w ) to the consumption-optimal operating frequency (f opt ) to set.

7. Cooling device (11) according to claim 6, wherein the control (10) is designed to set the operating frequency (f w) to vary again if the consumed electrical power (P) reaches or exceeds a predetermined threshold, in particular with respect to the previously detected minimum power (Pmin).

8. Cooling device (11) according to one of claims 6 to 7, wherein the control (10) is designed to control the operating frequency (f w ) again if the specified target lifting body stroke (A re f) has been changed.

9. Cooling device (11) according to one of claims 6 to 8, wherein the control (10) is designed to control the operating frequency (f w ) to vary again if a change in temperature and / or load reaches or exceeds a predetermined threshold.

10. Cooling device (11) according to one of claims 6 to 9, wherein the control (10) is designed to, when the operating frequency (f w) to specify a pre-calculated resonance frequency of the piston (3) or cylinder (2') as the initial value of the iteration process.

11. Cooling device (11) according to one of claims 6 to 10, wherein the control (10) is configured to carry out the iteration process continuously.

12. Cooling device (11) according to one of claims 6 to 10, wherein the control (10) is designed to adjust the set operating frequency (f w ) to vary again after a specified period of time.

13. Cooling device (11) according to one of the preceding claims, wherein the cooling device (11) is a household appliance with a cooling device, in particular a household cooling device such as a refrigerator, a freezer or a combination thereof, an air conditioner, a laundry appliance or a dishwasher.

14. Method for operating a cooling device (11) equipped with a refrigeration circuit operated by means of a linear compressor (1 , T), in which an operating frequency (f w ) of a piston (3) or cylinder (2') of the linear compressor (1 , T) is controlled so that an energy consumption (P) of the linear compressor (1 , T) is in the range of a minimum energy consumption (P m in).

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